The invention relates to a foldable multi-purpose ladder, and more particularly to a ladder having joints lockable in a plurality of operational positions.
Foldable multi-purpose ladders of the type cited above are already known. A foldable multi-purpose ladder is described in European Patent 0 090 198 in which the uprights are connected by joints arranged in pairs and lockable in several operational positions. The joints each have first and second joint elements pivotable around a common joint axis with each element consisting of left and right halves. The joint elements include guide portions which are insertable into hollow ladder uprights. The first joint element has a double-shell detent wheel which is concentric to the joint axis and which has in the area of its circumference radially extending grooves distributed in accordance with the operating positions, into which a spring-loaded detent piece can extend. The detent piece is longitudinally movable on the second joint element which surrounds the first joint element.
The detent piece can be lifted out of the respective grooves of the detent wheel by means of a release lever, pivotably disposed in bore holes in the left and right half of the second joint element. An operating lever, having arms connected by an eccentrically located bar, includes bore holes designed as bearings for receiving the release lever which also extends into the bore holes of the second joint element. The release levers of the pair of joint elements associated with the two uprights are connected with each other by means of a U-shaped operating bar. The detent piece has a locking bolt which extends approximately across the width of the second joint elenment and which is guided in a recess in the sidewalls of the second joint element. The detent piece has an adjoining guide member, the height of which is only slightly smaller than the clearance of the second joint element, but the width of which is larger than the width of the recess and which has a guide element for a pressure spring. The recesses in the side walls are each wider than the width of the locking bolt and form contact surfaces, or shoulders, which maintain the locking bolt in its released position. In the same manner the detent wheel with the grooves has a cam located next to the grooves which forms a stop face for the locking bolt of the detent piece.
Although this foldable multi-purpose ladder is of simple construction and is easy and safe to operate, it has the disadvantage that, if considerable force is exerted by the operating lever on the release lever, in particular the edges of the bearings provided on the bore holes of the arms of the release lever will be deformed, so that the secure support of the operating lever in the bearings of the release lever can no longer be assured.